n 80 --------------- 2*n - 1 n - 2 4 *5
1 - 2*n 2 - n n 4 *5 *80
2 - 4*n 2 - n n 2 *5 *80
4.0^(1.0 - 2.0*n)*5.0^(2.0 - n)*80.0^n
100
-2*n -n n 100*4 *5 *80